As methods for obtaining an epoxidized diene polymer by oxidizing a diene polymer as the target of an epoxidation, the following conventional methods have been known.
(1) A method of producing percarboxylic acid by reacting hydrogen peroxide with a lower carboxylic acid such as formic acid, acetic acid, etc., adding the percarboxylic acid to the reaction system as an epoxidizing agent to carry out an epoxidation reaction in the presence of or in the absence of a solvent.
(2) A method of epoxidizing by hydrogen peroxide in the presence of a catalyst such as an osmium salt, tungstic acid, etc. and a solvent.
Both of the above methods (1) and (2) are characterized by being carried out by dissolving the epoxidation target diene polymer in a solvent in order to conducting the epoxidation reaction efficiently.
However, these methods have complexity in the step of dissolving in a solvent, the step of washing treatment with water for removing carboxylic acids that are by-products after the epoxidation reaction and the step of removing solvent, thereby making the recovery of the product extremely difficult. Particularly, when the epoxidation target diene polymer is a rubber polymer, the epoxidized product has a high viscosity, and hence it is a problem that the product has extremely poor workability in handling it. And also concerning the form of the epoxidized polymer, some cases become a veil form that cannot be a raw material for molding such as powder, crumbs, pellets, etc. after the epoxidation. As a result, the use of the epoxidized polymer is often restricted in case of where the epoxidized polymer is added or kneaded to be used as a modifier.
With respect to a process for the production of an epoxidized diene polymer, for example, Japanese Unexamined Patent Publication No. 8-120022 proposes a method for obtaining an epoxidized diene polymer through the following steps: (1) the step of mixing a diene polymer or its partially hydrogenated product with an organic solvent to obtain a slurry or a solution of the polymer in an organic solvent; (2) the step of epoxidizing unsaturated carbon-carbon bonds present in a diene polymer by an epoxidizing agent; (3) the step of neutralizing and/or washing with water the solution thus obtained after the above epoxidation reaction; (4) the step of stripping a solution of the epoxidized block copolymer obtained through above steps having the concentration of the polymer is 5 to 50% by weight in the presence of a surfactant at the boiling point of the organic solvent, or at a temperature of the azeotropic point or more and 120° C. or less in case that the solvent and water give rise to azeotropy, thereby obtaining a slurry in which the polymer is dispersed in water; (5) the step of dewatering the crumb of the epoxidized diene block copolymer containing moisture thus obtained through the above steps to make the moisture content 1 to 30% by weight; and (6) the step of drying the epoxidized diene block copolymer through the above steps to make the moisture content 1% by weight or less.
Moreover, Japanese Unexamined Patent Publication No. 9-60479 discloses a process for the production of an epoxidized diene polymer, which process uses a screw extruder type squeezing dehydrator in the drying step of the above (6), and Japanese Unexamined Patent Publication No. 9-95512 proposes a process for the production of an epoxidized diene block copolymer, which process comprises supplying the epoxidized block copolymer obtained in the above step (3) to a evaporator, thereby evaporating the organic solvent directly to remove the organic solvent. Japanese Unexamined Patent Publication No. 8-104709 also proposes the process to improve the content of gels. However, these processes require large-sized facilities and hence they are not economical, so industrial implementation of these processes is difficult.
Furthermore, these processes are all the invention related to an epoxidized block copolymer produced by a homogeneous method that epoxidizes after dissolving a polymer as a raw material in a solvent. The characteristics of these processes for the production relate to a process for the production of a modified polymer having a quality that the content of gels is especially small. In addition, the epoxidized block copolymer obtained by these processes has a comparatively low softening point, thereby causing a problem during the production, processing, transportation or use of the copolymer, which problem is, for example, that the pellets of the epoxidized block copolymer cause blocking on the surfaces one another or tight adhesion to one another so that we have trouble handling them.
As a method for improving the above processes, Japanese Unexamined Patent Publication No. 9-165418 proposes a method of epoxidizing in a heterogeneous system by dispersing or suspending an organic polymer pellet and the like in an organic solvent system. However, the method uses ethyl acetate, hexane, etc. as organic solvents, which dissolve or swell a raw material resin, so pellets and the like are partly dissolved or swelled so that the pellets bring about a blocking state (mass state), thereby causing problems about facilities in the step of evacuating an epoxidized product.
Additionally, some polymer raw materials are dissolved in a solvent as an epoxidation proceeds, so the problem is caused that pellets give rise to blocking one another as the epoxidation proceeds in a similar manner as above. Besides, quantities of organic solvents are used as a solvent used in a reaction system, which is problematic from the viewpoint of the recovery operation of the organic solvents.
Japanese Unexamined Patent Publication No. 9-67502 proposes a method of adding a blocking inhibitor to the epoxidized copolymer obtained in a post-step.
Japanese Unexamined Patent Publication No. 9-208617 proposes a chemically modified diene polymer composition and a process for producing the same, which process comprises producing a polymer composition by epoxidizing a polymer in the state of particles having a size of 0.05 to 10 μm in water. However, this is the process for the production of the polymer composition, and no mention is made of the recovery performance of an epoxidized polymer or improvement in the blocking property of the epoxidized polymer.
Japanese Unexamined Patent Publication No. 10-316715 describes obtaining an aqueous dispersion of a polymer containing an epoxy-modified isoprene polymer, which the dispersion is excellent in mechanical stability as a dispersion and adhesiveness of a coat, by epoxidizing with peracetic acid an aqueous dispersion of an isoprene polymer in which isoprene units in the polymer are linked by trans-1,4 bond.
Japanese Unexamined Patent Publication No. 2000-44708 describes the invention related to a method for treating a surface of a rubber product in which an unvulcanized or vulcanized rubber product is surface-treated with an aqueous solution in the presence of a peracid to epoxidize the surface layer of the rubber product, thereby giving the non-adherence, lubricity and other barrier effects.